Woke up this morning and Finn is extremely pale and lethargic. He's just resting on top of the tallest plant and hasn't moved much since I woke up.
The tank is heated to 78 and I just did a 75% water change last night. He's in a divided 3 gallon (temporary for spring break) and Fleur seems just fine. Yesterday was fasting day and he doesn't look bloated. Other than that, he was building a bubblenest when I turned off the light last night.

Well normally they're in a 5 gallon cycled tank. I suppose it could be the differences between the water here at home and the water at school but wouldn't that have affected him a lot sooner rather than a week after I put him in this tank? I also acclimated them to our home water when I brought them back.
But I always do the same process when doing water changes. I let the water sit out and treat it. Take the fish out of the tank, remove the old water and put the new water in. Let it balance out the temperature and add them in later.